Dual band planar (and other types of) antenna systems often require the antenna to fit into ever-shrinking available spaces while maintaining key performance characteristics, such as high ohmic efficiency and dual-band operation in which two separate operating bands must be diplexed (separated) from one another. To achieve the desired performance, a hybrid combination of parallel-plate and waveguide transmission lines are often used as propagation media in the antenna design due to their superior bandwidth and ohmic efficiency characteristics. The waveguide transmission line (also referred to herein simply as ‘waveguide’) section is usually deployed in a corporate feed, traveling-wave feed, standing-wave feed, or other structure where multiple outputs are coupled to a common parallel-plate section. To support the hybrid combination of transmission lines and to support efficient performance over two widely separated frequency bands, there exists a coupling transition between the two-different media and diplexing (separation) of the two frequency bands.
Conventionally, substantial packaging volume is required to fit the numerous transmission lines and components necessary to draw-out two widely separated frequency bands from a broadband structure, such as a parallel-plate. Prior approaches propagate both bands through the parallel-plate, waveguide, and then coaxial medium before effecting the necessary frequency separation via a separately attached diplexing device.
Typical methods for drawing-out two widely separated frequency bands from a broadband structure such as a parallel-plate involves first transitioning to an array of relatively broadband, closely-spaced, ridged waveguide or coaxial transmission lines combined via a corporate feed network that results in a single waveguide or coaxial output, or alternatively, using a tapered horn to effect this transition (from parallel plate to a single output). Both approaches would use a separately attached waveguide or coaxial diplexer coupled to the single output to separate the two bands of interest. Each approach has its drawbacks either in terms of reduced efficiency, reduced bandwidth, reduced isolation, reduced frequency selectivity, added height profile, added design complexity or added manufacturing complexity.
For example, a common practice for transitioning high radio frequency (RF) power between a waveguide and a parallel-plate, when the waveguide is located in the same plane (level) as the parallel-plate structure and still required to carry a relatively wide band or two widely separated frequency bands, is through a ridged waveguide transition or a tapered horn transition. While the approaches are thin in height profile, in a practical case where multiple ridged waveguides or a tapered horn are used to feed a large parallel-plate region, feeding such a structure may be a challenge in the available space (which is usually confined to the total area provided by the product). Further, even with the extended bandwith afforded by the ridged-waveguide transmission-line structure, it is typically impractical to achieve lower-upper bandwidth separations of 2:1 or more, whereas the parallel-plate structure in accordance with the invention can support bandwidth separations up to 5:1.
Additionally, once the parallel-plate structure has been transitioned to a single waveguide or coaxial output, the output still carries two disparate frequency bands that must be separated from one another. This necessitates the use of additional diplexing hardware/components to effect such separation, further exacerbating the packaging and manufacturing challenges associated with such architecture.
In view of the aforementioned shortcomings, there is a need for a parallel-plate diplexer suitable for providing broad band separation of distinct and widely separated frequency bands propagating through parallel-plate transmission line.